Manufacture of carbon cloth



April 20, 1965 E. o. OHSOL 3,179,605

MANUFACTURE OF CARBON CLOTH Filed Oct. 12, 1962 R EG ENE RATED CELLULOSENON I I0 WASH ON RINSE IN WATER WASH WITH ORGANIC ACID NEL L A A E W'.I

AMMONIA WASH WITH WATER HEAT FAST TO 400 F.

HEAT SLOW 400E TO 500F.

HEAT GRADUALLY 500F. TO 800 F HEAT 800 F TO INVENTOR.

I500EOR ABOVE ERNEST O. OHSOL BY I? TIdEA/EVS United States Patent3,179,605 MANUFATITURE 0F CARBUN CLOTH Ernest 0. Ohsol, Wihnington,Del., assignor to Haveg Industries, Inc, a wholly-owned subsidiary ofHercules Powder Company, New Castle, Del., a corporation of DelawareFiled Oct. 12, 1962, Ser. No. 230,214 12 Claims. (Cl. 252-502) Thisinvention relates to the preparation of carbon fibers.

It has been proposed in the past to prepare carbon fibers fromcellulosic materials, e.g., Edison Patent 470,- 925, or more especiallyfrom regenerated cellulose, e.g., Soltes Patent 3,011,981 and AbbottPatent 3,053,775. However, it has been found difficult to obtainreproducible, good quality, high strength carbon fibers, e.g., in theform of yarn or cloth, by present procedures. While good qualityproducts are obtained in some runs, in other runs employing exactly thesame conditions the quality is poor.

Accordingly, it is an object of the present invention to prepare goodquality carbon fibers from regenerated cellulose, e.g., in the form ofyarn, cloth and the like, with reproducible results.

Another object is to prepare carbon fibers from regenerated cellulose inthe form of yarn and cloth having increased tensile strength.

A further object is to device an improved procedure for forming carbonfibers from regenerated cellulose.

Still further objects and the entire scope of applicability of thepresent invention will become apparent from the detailed descriptiongiven hereinafter; it should be understood, however, that the detaileddescription and specific examples, while indicating preferredembodiments of the invention, are given by way of illustration only,since various changes and modifications within the spirit and scope ofthe invention will become apparent to those skilled in the art from thisdetailed description.

It has now been found that these objects can be attained if regeneratedcellulose fibers, preferably in the form of cloth, are washed to asodium content below 25 parts per million (ppm) and preferably belowppm.

Sodium, generally in the form of salts, is introduced into theregenerated cellulose cloth or yarn during the processing and it hasbeen found essential to limit the sodium content in the mannerindicated. Certain special regenerated celluloses have a sodium contentbelow 25 ppm. and it is not necessary to employ the instant washingprocedure thereon.

As used in the present specification and claims the term regeneratedcellulose is intended to embrace fibers of viscose rayon, cuprammoniurnrayon and saponified cellulose ester rayon, e.g., saponified celluloseacetate rayon.

The invention will be best understood with reference to the accompanyingdrawing which is a diagrammatic illustration of the invention.

There is provided regenerated cellulose, preferably high tenacityrayons, in the form of cord, yarn, cloth or the like having a sodiumcontent above 25 ppm. While the sodium content can be reduced to below25 ppm. simply by copious washing with water, it has been foundpreferable to hasten the process utilizing the procedure in the flowsheet. Furthermore, while the most important factor is to reduce thesodium content below 25 ppm, most preferably below 10 ppm, it is alsodesirable to reduce the total ash below 200 ppm. and preferably below 50ppm.

The regenerated cellulose is first washed in water. The water mostpreferably contains a detergent. While potassium and ammonium containinganion detergents can be used, e.g., potassium lauryl sulfate, potassiumdodecyl benzene sulfonate, ammonium decyl benzene sulfonate, potassiumsulfosuccinate, ammonium di (Z-ethylhexyl) sulfosuccinate, it ispreferable to employ nonionic detergents such as Triton X-45, TritonX-ll4, Triton X-100, Triton X-102, Triton bl-101 and Triton N-l28. TheTritons of the X series are the reaction products of t-octylphenol withethylene oxide and the Tritons of the N series are reaction products oft-nonylphenol with ethylene oxide, i.e., the Tritons are alkylphenoxypolyalkoxyalkanols. In Triton X-45 there are five ethylene oxide groups,in Triton X-114 there are 7 to 8 ethylene oxide groups, in Triton X-100and Triton N-lOl there are 9 to 10 ethylene oxide groups, and in TritonX-102 and Triton N-128 there are 12 to 13 ethylene oxide groups.

There can be used corresponding surface active agents where the ethyleneoxide groups are replaced by propylene oxide groups, e.g., t-octylphenoloxypropylated with 10 propylene oxide groups. Other nonionic surfaceactive agents include sorbitan sesquioleate, sorbitan-polyethylene oxidemonolaurate, Ethofat 3 (the reaction product of ethylene oxide with amixture of palmitic, st-earic, oleic and linoleic acid), Ethofat 15 (thereaction product of ethylene oxide with a mixture of caprylic acid,capric acid and lauric acid), Ethomid 8 (the reaction product of theamides of caproic, caprylic and capric acids with ethylene oxide),Ethomid 18 (the reaction product of the amides of palmitic, stearic andoleic acid with ethylene oxide), polyethylene glycol stearate (Myrj 45),tertiary dodecyl polyethylene glycol thioether (Nonionic 218), Pluronics(condensation products of ethylene oxide with polypropylene glycol),sorbitan monopalmitate, polyethylene glycol lauryl ether (Brij). Thepreferred nonionic detergents are the higher alkyl phenol-alkylene oxideaddition products.

The detergent is used in an amount of 0.01 to 0.5% of the Wash water,usually 0.1%.

If a detergent is employed in the wash water, then the regeneratedcellulose is preferably rinsed in water to remove the detergent.

This is followed by an acid wash, generally at a pH of between 1 and 5.The acid wash contains a 1 to 10% solution of a water soluble organic orinorganic acid such as acetic acid, propionic acid, formic acid, oxalicacid, hydrochloric acid, phosphoric acid or sulfuric acid. Prefferablyacetic acid or hydrochloric acid is employed.

After the acid wash the regenerated cellulose is thoroughly washed withwater. As indicated in the drawing, the acid is preferably neutralizedfirst with ammonia prior to the water wash. The neutralization can beomitted but in such case considerably more Water is required in theWater Wash. The regenerated cellulose is then dried either at roomtemperature or more preferably in an oven at a temperature up to 212 F.

The dried regenerated cellulose, e.g., in the form of cloth or yarn, isthen converted to carbonized fibers, e.g., as cloth or yarn, either inknown manner such as shown in the Soltes Patent 3,011,981, December 5,1961, or Abbott Patent 3,053,775, September 11, 1962, or by an improvedprooedure as set forth below.

The dried regenerated cellulose which has been purified by removal ofthe sodium compounds and other noncellulosic materials is heated in anonoxidizing atmosphere in order to carbonize the fibers. As thenonoxidizing atposphere there can be used inert gases such as nitrogen,helium, argon or even a vacuum, e.g., 0.001 mm. Also, there can beemployed reducing gases such as hydrogen. Such procedures are known inthe art, such as Soltes and Abbott, for example. Preferably, however,there is em- .ployed ammonia since superior results can be attainedtherewith. The use of ammonia as the gas is an improvement over theprocedures which have been employed in the past.

'While ammonia gas is preferably employed in the present process forforming carbon fibers in which regenerated cellulose having a sodiumcontent above 25 ppm. is reduced to a sodium content below 25 p.p.m., itis also possible to use the ammonia gas to improve prior art processessuch as those of Soltes or Abbott.

The purified and dried regenerated cellulose in the nonoxodizingatmosphere is heated fairly rapidly, e.-g., in less than 2 minutes, to atemperature of 250 to 400 F., preferably between 300 and 400 F. It isthen heated slowly at a temperature of 250 F. to 500 F., most preferablybetween 300 and 500 F. While the time can be as short as 2 hours, it ispreferably at least 12 hours and can be as long as a week. The productis then gradually heated at a temperature of from 500 to 800 F. for 2 to24 hours or longer, usually for 4 to 12 hours. Next, the temperature israised from 800 to 1500 F. or above over a period of 2 to 1800 hours. Ata top temperature of 1500 F. the product has 94% carbon, at a toptemperature of 1800 -F. the product has 96.5 to 97.5% carbon, and at atop temperature of 2000" F. the product contains 98 to 99% carbon. Ifthe final temperature is elevated to 3500 F. or above, e.g., 5000 F.,the product is converted into graphite fibers or cloth.

It has been found desirable to use a final temperature of 1800 F.because the resulting fiber product, whether in the form of cord, yarnor cloth, is very strong and, in fact, has A the strength of theoriginal regenerated cellulose prior to carbonization. Such carbonizedproducts have a much higher strength than carbon fibers or cloths made(from rayons having higher sodium contents than 25 ppm.

Unless otherwise indicated, all parts and percentages are by weight.

Example 1 Viscose rayon yarn having a sodium content of 100 ppm. waswashed thoroughly with water until the sodium content was ppm. and thetotal ash content was below 50 p.p.m. The rayon was then dried at 212 F.The dry product was placed in an oven at 350 F. in a nitrogen atmosphereand heated at 350 to 500 F. for 24 hours. It was then heated in anitrogen atmosphere at a temperature of 500 to 800 F. for 6 hours andfinally heated in a nitrogen atmosphere at a temperature increasing from800 to 1800 F. over a period of 4 hours to obtain a carbon fiber producthaving 96.5% carbon.

Example 2 Wellington-Sears Fortisan-36 cloth, -i.e., instantaneouslysaponified cellulose acetate rayon (regenerated cellulose), having 3400filaments in the yarn and having x 20 threads per square inch and havinga sodium content above 50 p.p.rn. was washed with water containing 0.1%Triton X-l00, rinsed with water, washed with 2% aqueous acetic acid,neutralized with 6% aqueous ammonia and rinsed with water to give acloth product having 22 ppm. of sodium. This product wasdried at 212 F.and then converted to carbonized cloth by heating in a nitrogenatmosphere in the manner indicated below. The dry purified saponifiedcellulose acetate rayon was placed in an oven at 400 F. and heated at400 to 500 F. for 12 hours. It was then heated at a temperature of 500to 800 F. for 6 hours and finally heated at a temperature increasingirom 800 to 1800 F. over 12 hours to obtain a strong carbon cloth havinga carbon content of 97%, and a Mullen burst strength of 47 p.s.i.

Example 3 phere to obtain a product which was even better than that ofExample 2.

The process of Example 2 was repeated utilizing 2% hydrochloric acid inplace of the 2% acetic acid with similar results.

Example 5 The procedure of Example 2 was repeated but the re-' Example 6The procedure of Example 2 was repeated but the acid was with a mixtureof oxalic acid and acetic acid. The

sodium content was only reduced to 26.6 p.p.m. The Mullen burst strengthof the carbonized cloth was less than 19.

In another l'lll'l wherein the sodium content was only reduced to 23.4ppm. the Mullen burst strength was only 11.

Example 7 North American viscose rayon identified as Viscose CX658 wasemployed as the regenerated cellulose cloth. There were about 3400filaments in the yarn and there were about 20 x 20 threads per squareinch. The acid employed in the scouring was 5% acetic acid. The sodiumcontent of the cloth after purification and prior to carbonization was25 ppm. The final carbon cloth product had a Mullen burst strength of 15psi.

In another experiment when washing was carried out to a sodium contentof 6.4 ppm. and the viscose cloth carbonized, the Mullen burst strengthof the carbonized cloth was 62 psi. This further illustrates theimportance of sodium removal.

I claim:

1. A process of preparing carbon fibers of increased strength comprisingwashing regenerated cellulose fibers selected from the group consistingof viscose rayon, cu-

prammonium rayon and saponified cellulose acetate rayon having a sodiumcontent above 25 ppm. with water until the sodium content is below 25p.p.m., and then heating the regenerated cellulose in a nonoxidizingatmosphere, said heating being carried out at a temperature of 250 F. to500 F. for from 2 hours to a week, and then at a temperature of 500 to800 F. for 2 to 24 hours, and then at a temperature of 800 to 1500 F.for from 2 to 1800 hours to convert the fibers to carbon fibers.

2. A process according to claim 1 wherein the regenerated cellulosefibers are in the form of cloth. 0

3. A process according to claim 1 wherein at least a portion of thewater wash is an aqueous acid wash.

4. A process according to claim 3 wherein at least a portion of theWater wash is with water containing a nonionic detergent.

5. A process according to claim 1 wherein the regenerated cellulosefibers are washed to a sodium content below 10 ppm.

6. A process according to claim 5 wherein the regenerated cellulosefibers are in the form of cloth.

7. A process according to claim 1 wherein the nonoxidizing atmosphere isan inert gas.

8. A process according to claim 1 wherein at least a portion of thewater wash is with a member of the group consisting of acetic acid andhydrochloric acid.

9. A process according to claim 8 wherein after the acid wash theregenerated cellulose is washed with aqueous ammonia.

10. A process according to claim 1 wherein the heating at thetemperature of 500 F. and above is carried out in an ammonia atmosphere.

11. A process of preparing carbon fibers of increased strengthcomprising washing regenerated cellulose fibers selected from the groupconsisting of viscose rayon, cu-

pramrnonium rayon and saponified cellulose acetate rayon having a sodiumcontent above 25 ppm. with water until the sodium content is below 25p.p.m., and then heating the regenerated cellulose in a nonoxidizingatmosphere selected from the group consisting of nitrogen, helium,argon, ammonia, and a vacuum, said heating being carried out at atemperature of 250 F. to 500 F. for from 2 hours to a Week, and then ata temperature of 500 to 800 F. for 2 to 24 hours, and then at atemperature of 800 to 1500 F. for from 2 to 1800 hours to convert thefibers to carbon fibers.

6 12. A process according to claim 11 wherein the n0noxidizingatmosphere is ammonia vapor.

References Cited by the Examiner UNITED STATES PATENTS 3,011,981 12/6 1Soltes 252502 3,053,775 9/62 Abbott 252-421 3,116,975 l/64 Cross et al252-502 JULIUS GREENWALD, Primary Examiner.

1. A PROCESS OF PREPARING CARBON FIBERS OF INCREASED STRENGTH COMPRISINGWASHING REGENERATED CELLULOSE FIBERS SELECTED FROM THE GROUP CONSISTINGOF VISCOSE RAYON, CUPRAMMONIUM RAYOND AND SAPONIFIED CELLULOSE ACETATERAYON HAVING A SODIUM CONTENT ABOVE 25 P.P.M. WITH WATER UNTIL THESODIUM CONTENT IS BELOW 25 P.P.M., AND THEN HEATING THE REGENERATEDCELLULOSE IN A NONOXIDIZING ATMOSPHERE, SAID HEATING BEING CARRIED OUTAT A TEMPERATURE OF 250*F. TO 500*F. FOR FROM 2 HOURS TO A WEEK, ANDTHEN AT A TEMPERATURE OF 500 TO 800*F. FOR 2 TO 24 HOURS, AND THEN AT ATEMPERATURE OF 800 TO 1500*F. FOR FROM 2 TO 1800 HOURS TO CONVERT THEFIBERS TO CARBON FIBERS.